The Gospel of Thomas is a mid-2nd century Gnostic forgery, not a legitimate alternate gospel. It's a sayings collection borrowing from Matthew/Luke with added Greek philosophical content inconsistent with a 1st-century Jewish teacher.

Not conspiratorially excluded from the Bible — it's a Gnostic cult attempt to hijack Christianity, like modern JWs or Mormons. Dated mid-2nd century at earliest. Only one full copy exists. Contains bizarre sayings like "lucky is the lion that the human will eat." Gnostics believed the body was evil and salvation came through secret knowledge. Wesley Huff article linked for details.